1. Field of the Invention
The present invention relates to dielectric ceramic composition, used such as for dielectric layer of multilayer ceramic capacitor, and electronic device using the dielectric ceramic composition as dielectric layer.
2. Description of the Related Art
A multilayer ceramic capacitor, an example of electronic devices, for example, is manufactured by firing a green chip obtained by stacking alternately ceramic green sheets comprising pre-determined dielectric ceramic composition and internal electrode layers in a pre-determined pattern to be integrated. Since the internal electrode layer of multilayer ceramic capacitor is integrated with the ceramic dielectric body by firing, a material not reacted with the ceramic dielectric body needs to be selected. Therefore, as a material constituting the internal electrode layer, there has been no choice but using expensive noble metal such as platinum and palladium.
On the other, dielectric ceramic composition wherein inexpensive base metal such as nickel and copper can be used has been recently developed to attain significant cost reduction. Said dielectric ceramic composition is described such as in Japanese Unexamined Patent Application H11-92220: 100 parts by weight of main component comprising {BaO}mTiO2+M2O3+R2O3+BaZrO3+MgO+MnO wherein M2O3 is Sc2O3 and/or Y2O3 and R2O3 is selected at least one from Eu2O3, Gd2O3, Tb2O3 and Dy2O3, and 0.2 to 3.0 parts by weight of subcomponent comprising Li2O—(Si, Ti)O2—MO wherein MO is Al2O3 and/or ZrO2 or SiO2—TiO2—XO wherein XO is selected at least one from BaO, CaO, SrO, Mgo, ZnO and MnO.
An object of the above-described Japanese Unexamined Patent Application H11-92220 is to provide multilayer ceramic capacitor which shows good CR product under a high electric field strength as well as good DC bias characteristic and weatherability. However, according to the above-described Japanese Unexamined Patent Application H11-92220, specific permittivity of its capacitor is as low as 1500, resulting in a problem of downsizing and increasing capacitance of the capacitor. Moreover, thickness of inter layers between dielectric layers in examples of said H11-92220 is 30 μm, resulting in a problem of making said dielectric layers thinner.
Demands for downsizing and increasing capacitance of multilayer ceramic capacitor is rapidly growing due to the progress of downsizing, higher functioning and higher performance of recent electronic equipments. In order to meet these demands, measures such as improving dielectric materials to obtain higher specific permittivity or making dielectric layer thinner to obtain higher number of laminated layers are often taken, however, it becomes difficult to secure reliabilities, e.g. life expectancy, as said dielectric layers become thinner. Further, downsizing and higher functioning leads to higher density in electronic circuit, which develops fever at use and reveals higher temperature.
Furthermore, opportunities to use electronic devices, such as portable devices, outdoors are increasing. Therefore, demand for less change in characteristics by temperature change is more growing than the past. Multilayer ceramic capacitor is required to maintain high specific permittivity, e.g. 3500 or higher, with improved capacitance-temperature characteristic even when dielectric layer is made thinner. Capacitor of the above-described H11-92220, however, did not consider making dielectric layers thinner, therefore, it was difficult to obtain good temperature characteristic and maintain high specific permittivity simultaneously when said dielectric layers are made thinner.